Magnetic devices such as inductors and transformers are widely used in many electronic apparatuses such as power supply apparatuses or power adapters. Since the power supply apparatuses or power adapters are developed toward minimization and high power, the volumes of the magnetic devices for use in these electronic apparatuses are gradually reduced and the shapes thereof become flatter. Moreover, the magnetic devices can be directly arranged on a circuit board according to a surface mount technology (SMT). Consequently, such a magnetic device is also referred as a surface mount device (SMD).
Referring to FIG. 1(a), a schematic perspective view of a conventional SMD inductor mounted on a circuit board is illustrated. The SMD inductor 1 of FIG. 1(a) includes a magnetic core assembly 10, a winding coil 11, a first pin 12a and a second pin 12b. The pins 12a and 12b are coupled to both ends of the winding coil 11. The magnetic core assembly 10 has a receptacle 13. A magnetic pillar (not shown) is accommodated within the receptacle 13. The winding coil 11 is wound around the magnetic pillar and disposed within the receptacle 13. The first pin 12a and the second pin 12b are extended from the bottom surface of the magnetic core assembly 10. The first pin 12a and the second pin 12b are bonded onto corresponding contact portions 21a and 21b on the circuit board 2 according to a surface mount technology (SMT) so as to fix the SMD inductor 1 on the circuit board 2.
FIG. 1(b) is a schematic cross-sectional view of the SMD inductor shown in FIG. 1(a) taken from the cross-section A. As shown in FIG. 1(b), the SMD inductor 1 is mounted on the circuit board 2 according to a surface mount technology. The first pin 12a and the second pin 12b of the SMD inductor 1 is welded onto the contact portions 21a and 21b of the circuit board 2 by using a soldering material 22, thereby fixing the SMD inductor 1 on the circuit board 2. Since a gap 23 is formed between the SMD inductor 1 and the circuit board 2, the contact area between the SMD inductor 1 and the circuit board 2 is dependent on the pins 12a and 12b. Due to the small contact area between the SMD inductor 1 and the circuit board 2, the pins 12a and 12b fail to be firmly fixed onto the circuit board 2. Moreover, if the bottoms of the pins 12a and 12b are uneven or if the amount of the soldering material 22 is insufficient, the pins 12a and 12b also fail to be firmly fixed onto the circuit board 2 due to the poor solderability. In addition, the adhesion between the pins 12a, 12b and the contact portions 21a and 21b of the circuit board 2 may be insufficient because the pins 12a, 12b are readily shifted during the boning process. If no additional vibration-absorption structure is used to alleviate the stress when the electronic apparatus is suffered from an impact or collision, the SMD inductor 1 may be detached from the circuit board 2 in the vicinity of the pins 12a and 12b. As a consequence, the product reliability is impaired.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an improved surface mount magnetic device according to the present invention through wholehearted experience and research.